Radial bearing of the swash plate in known hydraulic machines is achieved using a number of rolling-contact (anti-friction) bearings. These bearings are mounted in two basic arrangements. The first arrangement comprises complete rolling bearings (for example roller bearings in serial arrangement). However, complete rolling bearings usually require larger built-in space, which has an unfavourable effect on the outer dimensions of the axial piston machine and on its total weight. U.S. Pat. No. 5,495,712 for example discloses a variable displacement type hydraulic system in which the swash plate is mounted by side projections upon respective roller bearings fixed inside the housing.
The second arrangement utilises partial roller bearings with a synchronizing mechanism for angular synchronization of the position of the retaining cage of the bearings relative to the swash plate. However, the partial rolling bearings are more expensive due to the arrangement of the retaining system and synchronizing mechanism. U.S. Pat. No. 5,390,584 discloses a follow up mechanism for a swash plate bearing. The swash plate is mounted on rollers in a bearing cage permitting the swash plate to tilt. In addition, angular movement of the first and second ends of a link moves the bearing cage to maintain the proper timing of the bearing cages.
A further disadvantage of both above-mentioned arrangements is that vibrations are transmitted through the housing towards the surroundings as a redundant noise.
A further known arrangement for radial bearing of a swash plate comprises a plurality of partial radial sliding bearings. These bearings are used either with partial hydrostatic balance or without hydrostatic balance. The disadvantage of both arrangements concerns friction in the bearing in some operating modes of the axial piston machine. This can be unsuitable with respect to safety in applications of hydrostatic drives for mobile machines. U.S. Pat. No. 4,710,107 relates to swashblock lubrication in axial piston fluid displacement devices. The rear of the swashblock 26 has a pair of arcuate bearing surfaces, which are supported by the device.
The friction can also have a negative effect on the control characteristics of the piston machine. Especially if it is a pump for hydrostatic drive of mobile machines, because the quality of some control properties of the hydrostatic drive may decrease.
The sliding support of a swash plate has better dampening properties. However, pulsating loading from pistons which is transmitted through the swash plate into the housing, has the same value as with rolling bearings, so that this loading is responsible for vibrations of the housing and for noise of the axial piston machine.
It is an object of the present invention to provide a variable displacement hydraulic machine that provides reduced vibrations and/or reduced noise and/or reduced size with respect to prior art hydraulic machines, or at least to provide a useful alternative.